Food webs from natural to production forests: composition, phylogeny and functioning

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Date

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Thesis Discipline

Ecology

Degree Grantor

University of Canterbury

Degree Level

Doctoral

Degree Name

Doctor of Philosophy

Habitat loss and fragmentation have been identified as the main drivers of biodiversity loss. These drivers increase the proportion of habitat edges and change the configuration of landscapes. Habitat edges are known to affect ecological patterns and processes, however, is still unknown how these boundaries affect the assemblage of interactions among species within a community, and particularly its structure. Food webs depict not only the composition of the community, but also the feeding links, which represent a measure of energy flow. Therefore, they can inform about the relationships among community diversity, stability, and ecosystem functions.
This thesis explores the effects of habitat edges across native vs. managed forests on the food web of a tri-trophic system comprising plants, herbivores (Lepidoptera larvae) and predators (parasitoids). Particularly, it addresses three main objectives: 1) how food webs at habitat edges are assembled from the species and interactions present in the adjoining habitats; 2) how phylogenetic diversity and the coevolutionary signal among interacting species change across a habitat edge gradient; and 3) whether the mechanisms driving community-wide consumption rates and the ecosystem service of pest control are related to structural characteristics of the food webs.
The key findings of this thesis are that, despite the composition of species and interactions of native and managed habitats merging at their interface, food-web structure did not arise as a simple combination of its adjacent habitat webs, potentially due to differential responses of organisms to habitat edges. Moreover, beyond taxonomic composition, the phylogenetic diversity and signal of coevolution among interacting species also change between habitat types, even though this did not translate to changes in consumption rates. Consumption rates and their stability increased with complementarity and redundancy in resource-use among predators.
This reflects how environmental changes such as habitat fragmentation can have an effect beyond composition per se, affecting the assemblage of species interactions and even potentially interfering with natural evolutionary processes. Therefore, using interaction-network approaches for determining the impacts of changes may shed light on the underlying mechanisms driving such changes, and help to develop landscape management plans that reduce negative effects on species assemblages.